We've got a new way of detecting what may be alien communications - light pulses.
Humans have been listening to radio frequencies for about 100 years now. This really isn't a great length of time when you're talking about interstellar communications. The Milky Way galaxy is about 100,000 light years across, so those first signals broadcast by Marconi have travelled only about 0.1 percent of the width of our own galaxy!
Of course, listening is a different matter. Alien civilizations, if they're out there, may have been broadcasting for thousands, or hundreds of thousands of years, so we could detect them from much further away, even from the far side of the galaxy.
But have we been wrong to look only at radio transmissions?
Breakthrough Listen, a group founded in 2015 to search for signs of alien life, has begun watching for short flashes of light - something they call "pulsed optical beacons". The logic goes that if we use light for communication - and we do - so might they. Light flashes are just as detectable as radio waves.
But faint - the telescope array used by Breakthrough Listen could detect a signal produced by humans' largest laser only as far as 2 per cent across the galaxy. Those aliens would have to be determined to communicate.
However, having read the "Three Body Problem" by Chinese writer Liu Cixin, this makes me a little uneasy.
Distant civilizations can't know whether another is hostile. Game theory would suggest that everyone ought to hide their existence from others. A strong military civilisation, faced with a weak but developing one, might decide that a early and decisive attack is the best defence.
Poignantly, whether we receive radio or light waves, there's the possibility of our overhearing chatter from a civilisation that no longer exists. Could they have been broadcasting the alien equivalent of:
Look on my Works, ye Mighty, and despair!